Theories of the origin of life

The universe came into being around 15 billion years ago through a big bang, a thermonuclear explosion of a dense entity proposed by Abbe Lemaitre in his Big Bang Theory in 1931. Subsequently, our solar system formed about 4.5 to 5 billion years ago from a gaseous cloud called the solar nebula, as Kant-Laplace’s Nebular Hypothesis suggested. Earth itself formed about 4.6 billion years ago and was initially hot and barren, along with the other planets in our solar system. However, Earth’s conditions changed, and life originated from non-living matter. As of now, Earth remains the only known place to support life. This event, known as biopoiesis (from Gk. bios, meaning life, and poiesis, meaning-making), occurred approximately 4000-4200 million years ago. Numerous scientists have proposed various theories to explain the origin of life. Let’s dig into this theory and learn how various philosophers and scientists describe the process of the origin of life.

Theory of special creation

According to a theory proposed by Hebrew et al. and supported by Father Suarez, life was created by a supernatural power, either all at once or over successive intervals. In the Bible’s Genesis, it is suggested that God created the entire world in six days. The first man, named Adam, was created from clay, and the first woman, Eve, developed from Adam’s twelfth rib. Similarly, in Hindu mythology, the creator god, Brahma, is said to have formed life. The first man was Manu, and the first woman was Shradha. However, it’s important to note that this theory is based on religious beliefs and accepted only through faith, not scientific evidence.

Theory of eternity (steady-state theory)

According to this theory, life has always existed and will always exist, just changing its form. The theory suggests that life has no beginning and will have no end. However, this idea was rejected because of evidence from fossils showing the origin and extinction of different species. Still, the supporters of this theory argued against this evidence by pointing to the coelacanth, a fish believed to be extinct but later found alive in Africa’s oceans after many years. Scientists like Preyer, Helmholtz, Hoyle, and Bondi believed in the immortality of life, meaning it is eternal. Pluto is also a supporter of this theory.

Theory of catastrophism

According to this theory, multiple creations have occurred, each preceded by catastrophic geological disturbances. These catastrophes were sudden and extensive disasters or misfortunes that completely wiped out existing life forms. Subsequently, new creations emerged, consisting of life vastly different from the previous ones. The main proponents of this idea were Georges Cuvier, a French scientist from 1769 to 1832, and Alcide d’Orbigny, who lived from 1802 to 1837.

Cosmozoic theory (theory of panspermia or spore theory)

The Cosmozoic theory, proposed by Richter in 1865 and supported by Arrhenius in 1908, is also known as the interplanetary theory. Richter believed in the everlasting nature of life, similar to the steady state theory, but he didn’t believe in the stability of life forms. According to this theory, life arrived on Earth from some other celestial body through resilient spores of simple organisms called cosmozoa, which were carried in meteorites or spaceships. These cosmozoa grew and evolved into various life forms upon finding favourable conditions on Earth. Interestingly, in 1961, meteorites containing fossils of alga-like microbes provided evidence for the existence of life on other planets. However, despite this finding, the Cosmozoic theory was ultimately discarded. The main reason for this rejection is the harsh conditions that living matter would have to endure, including extreme cold, dryness, and ultraviolet radiation from the sun, in order to make the journey to Earth.

Theory of spontaneous generation (theory of abiogenesis or auto-biogenesis)

The belief in the spontaneous generation of life from non-living matter was once a widely held theory. According to this idea, insects were thought to emerge from dew, while frogs and toads were believed to arise from moist soil under the influence of the sun. Butterflies were said to originate from cheese and flies and maggots were thought to come from decaying flesh. This theory found support among renowned figures such as Thales, Anaximander, Newton, and Van Helmont. However, over time, it faced challenges and was eventually disproved by the works of Francesco Redi in 1668, Abbe Lazzaro Spallanzani in 1768, and Louis Pasteur in 1867. These scientific pioneers conducted separate experiments that demonstrated conclusively that sterilized broth or flesh, when sealed, could not give rise to life even after being kept for several months. They found that life only originated when the broth or flesh was contaminated by pre-existing life, such as living microbes or their spores present in the air or eggs laid by flies. The theory of abiogenesis, which proposed that rotten meat or meat broth spontaneously gives rise to life, was debunked by these experiments. The evidence provided by Redi, Spallanzani, and Pasteur firmly established that life does not emerge spontaneously from non-living matter but rather requires the presence of pre-existing life for its origin.

Theory of biogenesis

The concept of biogenesis emerged as a response to the rejection of abiogenesis and auto biogenesis. Biogenesis proposes that life originates from pre-existing life, which Redi, Spallanzani, and Pasteur demonstrated through their experiments. However, despite its initial acceptance, this theory still left unanswered questions about the origin of life, leading to its eventual decline and disappearance.

Modern hypothesis or chemical theory of the origin of life

The modern theory of the origin of life, also known as abiogenesis, posits that life emerged from non-living matter through natural processes. While the exact sequence of events remains a subject of ongoing scientific investigation, the theory is supported by various lines of evidence and hypotheses. According to this modern theory, around 4 billion years ago, on a young and volatile Earth, simple organic compounds, such as amino acids and nucleotides, were formed through chemical reactions. These compounds then combined and interacted in complex ways, possibly aided by environmental factors like volcanic activity, lightning, and UV radiation, leading to the formation of more complex molecules, including RNA and DNA. Over time, these molecules began to self-replicate and undergo gradual changes through mutation and natural selection, giving rise to the first primitive life forms. These early life forms were likely simple and unicellular, but they laid the foundation for the evolution of more complex organisms over millions of years. While the modern theory of the origin of life provides a compelling framework, the precise details of how life emerged remain uncertain. Scientists continue to explore various hypotheses and conduct experiments to understand better the chemical and physical processes that could have led to the transition from non-life to life. In summary, the modern theory of the origin of life suggests that life arose from non-living matter through a gradual process of chemical evolution and self-replication, setting the stage for the incredible diversity of life forms that exist on Earth today. Haeckel, a Russian biochemist A.I. Oparin and an English biologist J.B.S. Haldane were advocating this theory.